Intermittent web advancing device

ABSTRACT

A pawl and ratchet web drive device is provided, the pawl being formed on the free end of a resilient furcation of a reciprocable, bifurcated plunger, the free end of the other furcation forming a back-up stop abuttable by the pawl to render it unyieldable when it is moved effectively against the trailing face of a tooth of a ratchet wheel to incrementally rotate the same, the pawl being deflectible laterally when it is retracted across the leading face of a tooth for performing a succeeding incremental movement. The device further includes a fixed detent interengageable with the teeth to prevent return rotation of the ratchet wheel and being deflectible out of its normal position when the wheel is moved by the pawl. Preferably, the parts of the ratchet mechanism are composed of hardened, molded plastic material having the inherent resiliency for performing the aforementioned deflections.

I United States Patent [[5] 3,677,452 Wallace [45] July 18,1972

[54] INTERMITTENT WEB ADVANCING Primary Examiner-Allen N. Knowles DEVICE Attorney-Kenneth L. Miller and Edwin W. Uren [72] Inventor: Barry L. Wallace, Garden City, Mich. [57] ABSTRACT [73] Assign: Burroughs Corporation Detroit Mich A pawl and ratchet web drive device is provided, the pawl [22] Filed: Dec. 28, 1970 being formed on the free end of a resilient furcation of a reciprocable, bifurcated plunger, the free end of the other fur- [21] Appl' 101885 cation forming a back-up stop abuttable by the pawl to render it unyieldable when it is moved effectively against the trailing [52] U.S. Cl ..225/ll, 83/247, 226/ 157. face of a tooth of a ratchet wheel to incrementally rotate the 226/90 same, the pawl being deflectible laterally when it is retracted [5 1 ll,- Cl. across the leading face of a [00th for performing a succeeding [58] Full! of Sear h ..226/l57, 90; 74/578, 577 incremental movement. The device further includes a fixed 74/ 5 77 577 R; 225/ H detent interengageable with the teeth to prevent return rotation of the ratchet wheel and being deflectible out of its nor- [56] References Cmd mal position when the wheel is moved by the pawl. Preferably, UNITED STATES PATENTS the parts of the ratchet mechanism are composed of hardened,

molded plastic material having the inherent resiliency for per- 3, 41 l Bloom et a] X fo ing the aforemenfioned deflecfins 3,448,249 6/1969 Jones, Jr. ..226/ 157 X 21 China, 13 Drawing Figures Patented July 18, 1972 4 Sheets-Sheet 2 4 ShetsShe-et 5 Patented July 18, 1972 Patented July 18, 1972 3,677,452

4 Sheets-Sheet 4 INTERMI'I'IENT was ADVANCING navrca BACKGROUND or THE INVENTION The invention relates to web driving devices and more particularly to ratchet drive mechanisms.

Prior art discloses intermittentweb advancing devices using pawl and ratchet drive mechanisms. A typical example uses a metal ratchet wheel which is incrementally rotatable in one direction by a metal pawl and is prevented from rotating in the oppositedirection' by a metal detent. The metal pawl is usually formed or mounted at the free end of an-elongated member which resiliently urges the pawl against the teeth of the ratchet wheel and yields as the pawl cams over the leading face of a tooth as it is retracted to abuttably engage the trailing face of the adjacent tooth. The ratchet wheel is advanced when. the pawl is moved in the opposite direction, thereby applying an abutting force against the trailing face of the adjacent tooth. The metal detent is commonly a resiliently supported member disposed to abut the trailing face of a tooth to prevent the ratchet wheel from rotating in a reverse direction as the pawl is being retracted or is otherwise disengaged. Since the pawl must be stiff enough to rotate theratchet wheel by relatively unyieldingly pushing against the trailing face of a tooth, the contact force between the pawl and the leading face of the tooth over which it cams must be relatively high. This higher forceincreases thefriction, which, in turn, results in an increased wear rate and also requires more driving force to retract the pawl. The use of metal components also introduces a lubrication requirement. The devices disclosed in the prior art include discrete parts assembled in effective combination, resulting in individual part manufacturing costs and assembly expenses.

SUMMARY OF THE INVENTION The invention resides in the provision of an intermittent web advancing device to incrementally advance a web of paper or similar material by means of a solenoid-reciprocatable pawl which is yieldably cammable out of the interdental spaces of an associated ratchet wheel upon retraction of the pawl and unyieldably supported upon advancement by a reinforcement homogeneously formed with it of a hardened, plastic material having an inherent flexibility. The ratchet wheel shares a common shaft with web driving rollers to communicate the angular advancement of the ratchet wheel by the pawl to the web. I

Accordingly, it is an object of the present invention to .provide an intermittent web advancing device which has relatively low friction between its moving parts.

It is another object of the invention to provide a device having a low rate of wear.

It is yet another object of the invention to provide a device which requires no lubrication between its relatively moving parts.

Still another object of the invention is to provide a device which is relatively inexpensive to manufacture and assemble.

An important aspect of the invention is the use of a pawl,

which is easily deflectible by the leading face of a ratchetwheel tooth as the pawl is retracted, in combination witha reinforcement, which unyieldingly supports the pawl when the latter is advanced against the trailing face of the tooth toinf crementally rotate the ratchet wheel. The contact force a between the pawl and the leading face of the tooth is thereby BRIEF DESCRIPTION OF THE DRAWINGS These and other objects, aspects and advantages of the invention will be' more clearly understood from the following description when read in conjunction with the accompanying drawings, in which:

FIG. I is a side view of an intermittent web advancing device embodying features of the invention;

FIG. 2 is a front view, partially fragmented, of the device of FIG. 1;

FIG. 3 is a side view similar to FIG. I, partly in section and taken along line 3-3 of FIG. 2;

FIG. 4 is a sectional view of the portion of the embodiment through and by which a web is advanced, such view taken along line 4-4 of FIG. 2;

FIG. 5 is a view similar to FIG. 4 and depicts the portion of the embodiment shown in an opened position in preparation of a manual web loading operation;

FIG. 6 is a non-sectional, partially fragmented view of the portion of the embodiment shown in FIG. 4;

,FIG. 7 is a non-sectional partially fragmented view of the portion of the embodiment shown in FIG. 5;

FIG. 8 is a partially fragmented, exploded, perspective view of the web advancing mechanism of the embodiment;

FIG. 9 is a partially fragmented, sectional view of the web advancing mechanism of the embodiment shown in its normal, rest position and having an index mark on an engaged ratchet wheel tooth to reference the wheels rotational advancement in subsequent figures, the section being taken along line 9-9 of FIG. 2;

FIG. 10 is a. partially fragmented, sectional view of the web advancing mechanism of the embodiment shown in a partially actuated position. and is taken along line 10-10 of FIG. 2;

FIG. 11 is a partially fragmented, sectional view of the web advancing mechanism of the embodiment shown in a fully actuated position and is taken along line 11-11 of FIG. 2;

FIG. 12 is a partially fragmented, sectional view of the web advancing mechanism of the embodiment shown in a partially restored position and is taken along line 12-12 of FIG. 2; and

FIG. 13 is a partially fragmented, sectional-view of the web advancing mechanism of the embodiment shown in a fully restored position, the ratchet wheel having been advanced one position as indicated by the indexed tooth, and is taken along line 13-13 of FIG. 2.

DESCRIPTION OF A PREFERRED EMBODIMENT Referring to FIGS. 1, 2 and 3, the intermittent web advancing device illustrated herein has a support structure or frame 20, a web driving pinch roller provision generally indicated at 22, a web grip release and deflecting head generally indicated at 24, a ratchet mechanism generally indicated at 26, and a source of power in the form of a solenoid 28.

With reference to FIGS. 1, 2 and 3, the frame 20 is preferably formed of a hardened plastic material cast in one piece and having basically a horizontally oriented base plate 30, a pair of upright side plates 32-32, a pair of upright guide plates 34-34 centrally disposed between the side plates, and

a pair of depending web guiding legs 36-36. The side plates extend upward from the base plate 30 and are mutually parallel. The guideplates 34 also extend upward from the base plate and are parallel to the sideplates. The web guiding legs 36 are formed of angular extensions of the side plates 32-32 and depend from the base plate 30 at adjacent corners thereof.

Referring now to FIGS. 4, 5 and 6, the web driving pinch rollers, generally indicated at 22, are composed of a pair of web driving rollers 38-38 and two pairs of smaller pressure rollers 40-40 and 42-42 all mounted on parallel extending axes. The web driving rollers 38-38 are spaced apart on a rotatable driving roller shafl 44 journaled in and extending between the upright side plates 32-32. Each roller 38 is discstruction serving to reduce manufacturing and assembly costs, a

and such plastic material requiring no lubrication betweenits relatively moving parts.

shaped and is preferably formed of a hardened plastic material. .Each includes a hub 46 affixed to the shaft 44 and a peripheral band or tire 48 having a relatively high coefficient of friction'(FIG. 8).

Forming part of the general assembly is the web grip release and deflecting head 24 having the dual function of changing the angular direction of the feed of a web and of assuming two positions, in one of which positions it facilitates manual loading of a web into the assembly and in the other position causes the pairs of pressure rollers 40-40 and 42-42 to tightly grip an inserted web for advancing it. Advantage is taken of the driving roller shaft 44 for providing a pivotal mounting for the web grip release and deflecting head 24 so that it may be shifted to either one of the two positions and releasably retained therein. As shown in FIGS. 1 through 7, the shaft 44 extends through and slightly beyond each of the side plates 32-32. The web grip release and deflecting head 24 is provided with side plates 52-52 which overlap the side plates 32-32 of the frame 20 and are pivotally mounted on the external extensions of the shaft 44. The head 24 has an arcuate inner surface 54 which conforms to the curvature of the web driving rollers 38-38 and has a center of curvature coincident with the axis of rotation of the shaft 44, thereby defining a web guideway 55 between its arcuate inner surface and the adjacent surfaces of the frame 20. The trailing edge 56 of the arcuate inner surface 54 is preferably serrated to form a web tear.

Carried by the web grip release and deflecting head 24 and extending parallel to the driving roller shaft 44 are a pair of shafts 58 and 60, the former being located near the leading edge 62 and the latter near the trailing edge 56 of the head 24. The two shafts 58 and 60 describe a right angle with respect to the driving roller shaft 44, the shaft 60 normally overlying the latter. The two shafts 58 and 60 reside, at their extremities, in slots 64 in the head 24, as best shown in FIGS. 6 and 7. The pair of pressure rollers 40-40 are rotatably mounted on the shaft 58, and each roller is positioned peripherally adjacent a respective one of the pair of web driving rollers 38-38. The pair of pressure rollers 42-42 are rotatably mounted on the shaft 60, and each roller is positioned to overlie a respective one of the pair of web driving rollers. The pressure rollers 40-40 and 42-42 are held in eflective contact with the web driving rollers 38-38 by a pair of reed-type springs 66-66, the ends of which resiliently engage the shafts 58 and 60, and the central portions of which are affixed to the head 24 by screws 68. The peripheral points of contact between the pressure rollers and the web driving rollers fall substantially central to the web guideway 55, the pressure rollers being urged toward the web driving rollers by the springs 66-66.

As illustrated by FIGS. 4 through 7, the web grip release and deflecting head 24 is pivotable over a small angle about the shaft 44 from its normal position as shown by FIGS. 4 and 6 to its web loading position as shown by FIGS. and 7. Disposed on each of the side plates 32-32 of the frame 20 adjacent each end of the shaft 58 is one of a pair of cams 70-70. Similar cams 72-72 are so disposed adjacent the ends of the shaft 60. These cams are shaped to effectively engage the respective ends of the two shafts when the head 24 is pivoted to its web loading position to shift the pressure rollers 40-40 and 42-42 away from the web driving rollers 38-38. The cams 72-72 are each notched as at 74-74 to receive the ends of the shaft 60 when the head 24 has been fully pivoted to its web loading position, thus serving to retain the head in this position under the influence of the springs 66-66. The head 24 is retained in its normal position under the same influence, the ends of the shaft 60 normally residing in their respective slots 64 at a level slightly lower than the steps of the cams 72- 72.

As illustrated by FIGS. 8 through 13, the ratchet mechanism generally indicated at 26 has a ratchet wheel 76, a resiliently stationary pawl 78, and a reciprocatable pawl 80. The ratchet wheel is affixed to the web driving roller shaft 44 midway between the web driving rollers 38-38. The stationary pawl 78 is an elongated projection of and is parallel to the upper edge of one of the upright guide plates 34-34, and its free end effectively engages the trailing faces of the teeth of the ratchet wheel 76. Attached to one of the side plates 32-32 of the frame 20 is the solenoid 28. Extending from the solenoid toward the ratchet wheel is the free end of a ferromagnetic solenoid armature 84. Attached to the free end of the armature 84 and forming an extension thereof is a bifurcated plunger 86 preferably formed of a one-piece, hardened plastic material having an inherent flexibility. The bifurcated end of the plunger 86 extends tangentially toward the ratchet wheel 76, passing between and being slidably guided by the pair of guide plates 34-34. A helical spring 88, partially compressed between shoulders of the plunger 86 and the face of the solenoid 28, urges the plunger tangentially toward the ratchet wheel, the solenoid, when energized, being actuatable to pull the plunger in the opposite direction. An adjustable plunger travel stop 90 is adjustably mounted on the frame 20, extending therethrough to be abutted by the free end of the plunger 86 and thereby limit its throw in the direction of the ratchet wheel 76.

The free end of one of the plunger furcations forms a reinforcement 92, and the free end of the other extends beyond the reinforcement and forms the pawl projecting at right angles thereby. The plunger is oriented such that the furcation forming the reinforcement is disposed between the other furcation and the ratchet wheel, the pawl 80 extending upward past the reinforcement to effectively engage the teeth of the ratchet wheel 76.

OPERATION OF THE INVENTION With reference to FIGS. 4 through 7, the web loading operation of the intermittent web advancing device may be described. When a web 96, typically comprising a record paper, is to be inserted into the device, the web grip release and deflecting head 24 is pivoted forward (counterclockwise) to its web loading position as shown by FIGS. 5 and 7. As it is pivoted, the ends of the two shafts 58 and 60 will be deflected in their slots 64 against the resilient biasing of the springs 66 as the shaft ends ride over the steps of the cams 70-70 and 72- 72, respectively, mounted on the side plates 32-32 of the frame 20. As the ends of the shafts ride over these earns, the pressure rollers 40-40 and 42-42 will be forced away from their resiliently biased, peripheral contact with the web driving rollers 38-38. When the head 24 has been swung into its web loading position as shown in FIGS. 5 and 7, clearance will have been provided between the web driving rollers 38-38 and the pressure rollers 40-40 and 42-42 to permit the insertion of a web into the guideway 55 defined between the arcuate inner surface 54 of the head 24 and the adjacent surface of the frame 20. As the web 96 is inserted upward into the guideway 55, it is deflected by the arcuate inner surface of the head into a path substantially at right angles to its direction of insertion and around the peripheries of the web driving rollers 38-38 until it emerges from the web guideway at the trailing edge 56 of the head 24.

After the web 96 has been thus inserted and aligned in the web guideway 55 as desired, the head 24 is swung back to its normal position as shown by FIGS. 4 and 6. As the head is so pivoted, the shafts 58 and 60 descend the steps of the cams 70-70 and 72-72, respectively, allowing the pressure rollers 40-40 and 42-42 to resiliently press the web 96 against the web driving rollers 38-38. Any excess length of web extending past the guideway 55 may at this or any other time the web is not being advanced be sheared off by being pulled sharply upward against the web tear formed by the serrated trailing edge 56 of the head 24.

Referring now to FIGS. 8 through 13, the web advancing operation of the invention may be described. A web 96 positioned in the web guideway 55 may be advanced one increment by electrically energizing the solenoid 28 for a time adequate for it to fully attract its armature 84, and then deenergizing the solenoid to thereby allow its armature to return to its normal position under the influence of the helical spring 88. As the solenoid 28 is energized, thereby attracting its armature 84, the bifurcated plunger 86 attached to the armature is also moved in the same direction. As the plunger is retracted, the pawl 80 formed at the end of one of its furcations and normally residing between two adjacent teeth on the ratchet wheel 76 will also be pulled in this direction. As the pawl travels over the leading face of a tooth on the ratchet wheel, it will be forced normally away therefrom in opposition to the resilient influence of the flexible body of the elongated furcation at the end of which the pawl is formed, as shown in FIG. 10. As the pawl passes the peak of the tooth on which it is riding, it will be resiliently forced into contact with the leading face of the next tooth on the ratchet wheel. At this point, the plunger'86 will have reached its maximum retracted position, as shown in FIG. 11.

Upon the subsequent de-energization of the solenoid 28, the helical spring 88 will force the plunger 86 back to its original position. The pawl 80 will be forced against the trailing face of the original tooth on the ratchet wheel 76. As the pawl is forced forward by the motion of the plunger, the opposing force exerted on the pawl by the trailing face of the tooth on the ratchet wheel will force the pawl back against its reinforcement 92 formed at the end of the other furcation of the plunger, as shown in FIG. 12. The reinforcement provides unyielding support for the pawl, which, due to the motion of the plunger, will force the ratchet wheel to rotate one increment, the size of which is proportional to the length of travel of the pawl.

As the ratchet wheel 76 is rotated, the leading face of the tooth anterior to the one being pushed by the pawl 80 will force the free end of the stationary pawl 78 downward, as shown in FIG. 12. Just before the pawl reaches its normal rest position, the peak of the aforementioned anterior tooth will pass the end of the stationary pawl 78, permitting it to restore itself to its original position, its end now being positioned effectively behind the trailing face of the tooth which just deflected it. In this position, the end of the stationary pawl acts as a stop to prevent the ratchet wheel from rotating in a direction opposite that in which it has just been driven.

As the ratchet wheel 76 is rotated by the pawl 80, the driving roller shaft 44 to which it is affixed is also rotated in the same direction. The web driving rollers 38-38, also attached thereto, will likewise rotate in the same direction. As the web driving rollers rotate, the web 96 forced thereagainst by the pressure rollers 4040 and 42-42 will be advanced an amount proportional to the amount of rotation of the web driving rollers. As can be readily seen, the web may be incrementally advanced to any subsequent position merely by intermittently energizing the solenoid 28.

While the intermittent web advancing device has been shown and described in considerable detail, it should be understood that many changes and variations may be made thereto without departing from the spirit and scope of the invention.

What is claimed is:

1. An intermittent web advancing device including:

a support structure;

a web grip release and deflecting head mounted on said support structure and providing a web guideway forming a web path therewith;

a rotatable shaft journaled in said support structure;

one or more web driving rollers afl'ixed to said shaft in spaced-apart relationship;

a like number of pressure rollers journaled in said web grip release and deflecting head, each pairing with and resiliently bearing upon an individual one of said web driving rollers, the points of contact of said paired rollers being in the web guideway;

a ratchet wheel affixed to said rotatable shaft;

a detent member on said support structure effectively engaging the teeth of said ratchet wheel to prevent rotation in one direction; and

a reciprocatable, bifurcated plunger slidably guided by said support structure tangentially toward and away from said ratchet wheel and being actuatable in one direction and resiliently biased in the other direction, said plunger having the free end of one furcation forming a reinforcement and the free end of the other furcation forming a pawl, the pawl being abuttably held by said reinforcement effectively against the trailing face of a tooth of the ratchet wheel as said plunger is moved toward the ratchet wheel to thereby rotate the ratchet wheel and driving rollers, the pawl being also flexibly cammable by the leading face of the tooth upon movement of said plunger away from said ratchet wheel.

2. An intermittent web advancing device as defined by claim 1 wherein said web grip release and deflecting head has an arcuate inner surface, the center of curvature of the arcuate surface and the axis of rotation of said shaft being coincident.

3. An intermittent web advancing device as defined by claim 2 wherein said web grip release and deflecting head is pivotably mounted on said support structure at points on the center of curvature of the arcuate inner surface of said web grip release and deflecting head.

4. An intermittent web advancing device as defined by claim 3 and additionally comprising an adjustable plunger travel stop mounted on said support structure adjacent the bifurcated end of said plunger and effectively abuttable therewith to limit the throw of said plunger.

5. An intermittent web advancing device as defined by claim 4 wherein said detent member comprises an elongated and flexible projection of said support structure disposed to effectively engage the trailing face of a tooth on said ratchet wheel to prevent reverse rotation thereof, said detent member being deflectible out of engagement with said ratchet wheel by a subsequent tooth thereof as said ratchet wheel is rotated in the desired direction.

6. An intermittent web advancing device as defined by claim 5 and additionally comprising a pair of elongated projections extending from said support structure and parallel but spaced apart for slidably guiding said plunger therebetween.

7. An intermittent web deflecting device as defined by claim 6 wherein said plunger is actuatable in a direction tangentially away from and resiliently biased in a direction tangentially toward said ratchet wheel.

8. An intermittent web deflecting device as defined by claim 7 wherein said plunger is actuatable by an electrical solenoid mounted on said support structure.

9. An intermittent web advancing device as defined by claim 4 wherein the trailing edge of said web grip release and deflecting head is serrated to form a web tear.

10. An intermittent web advancing device including:

a support structure shaped to provide a guideway forming a web path;

a rotatable shaft journaled in said support structure;

one or more web driving rollers afiixed to said shaft in spaced-apart relationship and jointly rotatable therewith;

a ratchet wheel affixed to said rotatable shaft;

a stationary pawl on said support structure effectively engaging the teeth of said ratchet wheel to prevent rotation in one direction; and

a reciprocatable, bifurcated plunger slidably guided by said support structure tangentially toward and away from said ratchet wheel and being actuatable in one direction and resiliently biased in the other direction; said plunger having the free end of one furcation forming a reinforcement and the free end of the other furcation forming a pawl, the pawl being abuttably held by said reinforcement effectively against the trailing face of a tooth of the ratchet wheel as said plunger is moved toward the ratchet wheel to thereby rotate the ratchet wheel and driving rollers, the pawl being also flexibly cammable by the leading face of the tooth upon movement of said plunger away from said ratchet wheel.

11. An intermittent web advancing device as defined by claim 10 wherein a web deflecting head is mounted on said supporting structure and cooperates with said web driving rollers to provide a bend in the web path.

12. An intermittent web advancing device as defined by claim 11 wherein said web deflecting head comprises pressure rollers cooperably associated with said driving rollers and wherein said head is movable to a first position to permit a web to be moved relative to said web driving rollers to facilitate web loading and movable to a second position to press a web against said web driving rollers by means of said pressure rollers.

13. An intermittent web advancing device as defined by claim 12 and additionally comprising a plurality of cams mounted on said support structure and operable upon the movement of said web deflecting head to the first position to force said pressure rollers away from said web driving rollers to facilitate the manual advancement of a web therebetween.

14. An intermittent web advancing device as defined by claim 13 wherein said web deflecting head has an arcuate inner surface, the center of curvature of the arcuate surface and the axis of rotation of said web driving rollers being coincident.

15. An intermittent web advancing device as defined by claim 14 wherein said web deflecting head is mounted on said support structure and is pivotable between the first position and the second position about an axis coincident to the axis of rotation of said web driving rollers.

16. An intermittent web advancing device as defined by claim wherein said support structure and said stationary pawl are formed by one piece of a hardened plastic material having an inherent flexibility.

17. An intermittent web advancing device as defined by claim 16 wherein said ratchet wheel is formed of a hard plastic.

18. An intermittent web advancing device having a ratchet mechanism including a support structure, a ratchet wheel rotatably mounted on said support structure, and a reciprocatable, bifurcated plunger movable tangentially toward and away from said ratchet wheel, said plunger having the free end of a first furcation forming a pawl extending at right angles to its direction of motion for entering into an interdental space of the ratchet wheel, the free end of the second furcation terminating short of an abuttable reinforcement for the pawl.

19. An intermittent web advancing device as defined by claim 11 wherein the first furcation of said plunger is inherently flexible to permit the pawl formed at the free end thereof to be cammed radially out of engagement with a tooth of said ratchet wheel as said plunger is moved tangentially away therefrom.

20. An intermittent web advancing device as defined by claim 19 wherein the abuttable free end of the second furcation of said plunger unyieldingly reinforces the pawl formed on the free end of the first furcation of said plunger as the pawl is forced against the back face of a tooth on said ratchet wheel as said plunger is moved tangentially theretoward.

21. An intermittent web advancing device as defined by claim 20 wherein said plunger is formed of a hardened plastic material having an inherent flexibility.

* a: t k 

1. An intermittent web advancing device including: a support structure; a web grip release and deflecting head mounted on said support structure and providing a web guideway forming a web path therewith; a rotatable shaft journaled in said support structure; one or more web driving rollers affixed to said shaft in spacedapart relationship; a like number of pressure rollers journaled in said web grip release and deflecting head, each pairing with and resiliently bearing upon an individual one of said web driving rollers, the points of contact of said paired rollers being in the web guideway; a ratchet wheel affixed to said rotatable shaft; a detent member on said support structure effectively engaging the teeth of said ratchet wheel to prevent rotation in one direction; and a reciprocatable, bifurcated plunger slidably guided by said support structure tangentially toward and away from said ratchet wheel and being actuatable in one direction and resiliently biased in the other direction, said plunger having the free end of one furcation forming a reinforcement and the free end of the other furcation forming a pawl, the pawl being abuttably held by said reinforcement effectively against the trailing face of a tooth of the ratchet wheel as said plunger is moved toward the ratchet wheel to thereby rotate the ratchet wheel and driving rollers, the pawl being also flexibly cammable by the leading face of the tooth upon movement of said plunger away from said ratchet wheel.
 2. An intermittent web advancing device as defined by claim 1 wherein said web grip release and deflecting head has an arcuate inner surface, the center of curvature of the arcuate surface and the axis of rotation of said shaft being coincident.
 3. An intermittent web advancing device as defined by claim 2 wherein said web grip release and deflecting head is pivotably mounted on said support structure at points on the center of curvature of the arcuate inner surface of said web grip release and deflecting head.
 4. An intermittent web advancing device as defined by claim 3 and additionally comprising an adjustable plunger travel stop mounted on said support structure adjacent the bifurcated end of said plunger and effectively abuttable therewith to limit the throw of said plunger.
 5. An intermittent web advancing device as defined by claim 4 wherein said detent member comprises an elongated and flexible projection of said support structure disposed to effectively engage the trailing face of a tooth on said ratchet wheel to prevent reverse rotation thereof, said detent member being deflectible out of engagement with said ratchet wheel by a subsequent tooth thereof as said ratchet wheel is rotated in the desired direction.
 6. An intermittent web advancing device as defined by claim 5 and additionally comprising a pair of elongated projections extending from said support structure and parallel but spaced apart for slidably guiding said plunger therebetween.
 7. An intermittent web deflecting device as defined by claim 6 wherein said plunger is actuatable in a direction tangentially away from and resiliently biased in a dIrection tangentially toward said ratchet wheel.
 8. An intermittent web deflecting device as defined by claim 7 wherein said plunger is actuatable by an electrical solenoid mounted on said support structure.
 9. An intermittent web advancing device as defined by claim 4 wherein the trailing edge of said web grip release and deflecting head is serrated to form a web tear.
 10. An intermittent web advancing device including: a support structure shaped to provide a guideway forming a web path; a rotatable shaft journaled in said support structure; one or more web driving rollers affixed to said shaft in spaced-apart relationship and jointly rotatable therewith; a ratchet wheel affixed to said rotatable shaft; a stationary pawl on said support structure effectively engaging the teeth of said ratchet wheel to prevent rotation in one direction; and a reciprocatable, bifurcated plunger slidably guided by said support structure tangentially toward and away from said ratchet wheel and being actuatable in one direction and resiliently biased in the other direction; said plunger having the free end of one furcation forming a reinforcement and the free end of the other furcation forming a pawl, the pawl being abuttably held by said reinforcement effectively against the trailing face of a tooth of the ratchet wheel as said plunger is moved toward the ratchet wheel to thereby rotate the ratchet wheel and driving rollers, the pawl being also flexibly cammable by the leading face of the tooth upon movement of said plunger away from said ratchet wheel.
 11. An intermittent web advancing device as defined by claim 10 wherein a web deflecting head is mounted on said supporting structure and cooperates with said web driving rollers to provide a bend in the web path.
 12. An intermittent web advancing device as defined by claim 11 wherein said web deflecting head comprises pressure rollers cooperably associated with said driving rollers and wherein said head is movable to a first position to permit a web to be moved relative to said web driving rollers to facilitate web loading and movable to a second position to press a web against said web driving rollers by means of said pressure rollers.
 13. An intermittent web advancing device as defined by claim 12 and additionally comprising a plurality of cams mounted on said support structure and operable upon the movement of said web deflecting head to the first position to force said pressure rollers away from said web driving rollers to facilitate the manual advancement of a web therebetween.
 14. An intermittent web advancing device as defined by claim 13 wherein said web deflecting head has an arcuate inner surface, the center of curvature of the arcuate surface and the axis of rotation of said web driving rollers being coincident.
 15. An intermittent web advancing device as defined by claim 14 wherein said web deflecting head is mounted on said support structure and is pivotable between the first position and the second position about an axis coincident to the axis of rotation of said web driving rollers.
 16. An intermittent web advancing device as defined by claim 10 wherein said support structure and said stationary pawl are formed by one piece of a hardened plastic material having an inherent flexibility.
 17. An intermittent web advancing device as defined by claim 16 wherein said ratchet wheel is formed of a hard plastic.
 18. An intermittent web advancing device having a ratchet mechanism including a support structure, a ratchet wheel rotatably mounted on said support structure, and a reciprocatable, bifurcated plunger movable tangentially toward and away from said ratchet wheel, said plunger having the free end of a first furcation forming a pawl extending at right angles to its direction of motion for entering into an interdental space of the ratchet wheel, the free end of the second furcation terminating short of an abuttable reinforcement for the pawl.
 19. An intermittent web advAncing device as defined by claim 11 wherein the first furcation of said plunger is inherently flexible to permit the pawl formed at the free end thereof to be cammed radially out of engagement with a tooth of said ratchet wheel as said plunger is moved tangentially away therefrom.
 20. An intermittent web advancing device as defined by claim 19 wherein the abuttable free end of the second furcation of said plunger unyieldingly reinforces the pawl formed on the free end of the first furcation of said plunger as the pawl is forced against the back face of a tooth on said ratchet wheel as said plunger is moved tangentially theretoward.
 21. An intermittent web advancing device as defined by claim 20 wherein said plunger is formed of a hardened plastic material having an inherent flexibility. 